The present invention relates to the field of overrunning, one-way clutches (OWC) and one-way brakes (OWB). More particularly the invention relates to a dual-mode, one-way torque transmitting device, at least one of whose operating modes is actuated by fluid pressure, either hydraulic or pneumatic.
Conventional one-way clutches or brakes for producing a one-way drive connection between inner and outer races of the clutch include sprags or rollers for releasably driveably connecting the races and the components of a mechanical assembly connected to the races. Such clutches are commonly used in the powertrain or driveline of an automotive vehicle. One-way clutches perform satisfactorily in many cases, but certain applications, such as those in which large magnitudes of torque are transmitted by the clutch, or those that provide only a small space for the clutch, require one-way clutches other than conventional sprag-type or roller-type clutch to meet desire requirements.
Conventional one-way clutch assemblies have at least one sprag or roller, which driveably locks two notched or pocketed races together mutually in one rotary direction and allows the races to rotate freely in the other direction. Rocker and sprag type one-way clutch assemblies can increase the torque capacity for a given package size compared to those of a roller-type clutch, but they are generally limited in torque transmitting capacity by the magnitude of the contact or bearing stresses caused by contact of the rockers or sprags with the races.
To overcome these and other difficulties, a one-way overrunning clutch described in U.S. Pat. No. 5,070,978 includes a drive member and a driven member, which are mounted for clockwise and counterclockwise rotation about a common axis. The drive member includes a planar drive face, normal to the common axis, which connects with a source of power for rotating the planar drive face either clockwise or counterclockwise. The driven member includes a planar driven face, positioned in close proximity to and in confronting relationship with the drive face. The drive and driven members are coupled to one another through a series of pockets in one of the drive faces, and a plurality of cooperating struts carried by the other face, such that when the drive member is driven counterclockwise, it drives the driven member with it. When the drive member is driven clockwise, it does not drive the driven member, but rotates freely relative to the driven member. Column stability of the strut, which transmits the torsion load between the races, is an importance factor in the design.
Conventional one-way clutches develop relatively large magnitudes of hoop stress in the races when torque is transmitted through the clutch; therefore, the races of conventional one-way clutches are formed of bearing grade steel in order to withstand the operating hoop stress.
Conventional one-way clutches are able to transmit torque in only one rotary direction. Consequently, in an automatic transmission application, a second OWC or brake is required to provide coast braking operation as well as reverse gear operation. The proposed device eliminates coast and reverse clutches in the transmission and replaces them with a hydraulically activated rocker clutch. This device is essentially two rocker clutches in a single device. One rocker clutch is conventionally/passively activated and released while the second clutch is hydraulically controlled via the transmission hydraulic control system and can be selectively activated and de-activated.
A need exits, therefore, for a low cost, selectable, dual mode, one-way torque transmitting device that produces low operating bearing stresses and can be formed readily from powered metal. The device should occupy little space, minimize in-service noise, and require little or no machining. Preferably, the desired device would include features that facilitate its assembly in a drive system.